How to Register Event Listeners and Subscribers
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How to Register Event Listeners and Subscribers
Doctrine packages a rich event system that fires events when almost anything
happens inside the system. For you, this means that you can create arbitrary
services and tell Doctrine to notify those
objects whenever a certain action (e.g. prePersist) happens within Doctrine.
This could be useful, for example, to create an independent search index
whenever an object in your database is saved.
Doctrine defines two types of objects that can listen to Doctrine events: listeners and subscribers. Both are very similar, but listeners are a bit more straightforward. For more, see The Event System on Doctrine's website.
The Doctrine website also explains all existing events that can be listened to.
Configuring the Listener/Subscriber
To register a service to act as an event listener or subscriber you just have to tag it with the appropriate name. Depending on your use-case, you can hook a listener into every DBAL connection and ORM entity manager or just into one specific DBAL connection and all the entity managers that use this connection.
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doctrine:
dbal:
default_connection: default
connections:
default:
driver: pdo_sqlite
memory: true
services:
my.listener:
class: AppBundle\EventListener\SearchIndexer
tags:
- { name: doctrine.event_listener, event: postPersist }
my.listener2:
class: AppBundle\EventListener\SearchIndexer2
tags:
- { name: doctrine.event_listener, event: postPersist, connection: default }
my.subscriber:
class: AppBundle\EventListener\SearchIndexerSubscriber
tags:
- { name: doctrine.event_subscriber, connection: default }Creating the Listener Class
In the previous example, a service my.listener was configured as a Doctrine
listener on the event postPersist. The class behind that service must have
a postPersist method, which will be called when the event is dispatched:
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// src/AppBundle/EventListener/SearchIndexer.php
namespace AppBundle\EventListener;
use Doctrine\ORM\Event\LifecycleEventArgs;
use AppBundle\Entity\Product;
class SearchIndexer
{
public function postPersist(LifecycleEventArgs $args)
{
$entity = $args->getEntity();
// only act on some "Product" entity
if (!$entity instanceof Product) {
return;
}
$entityManager = $args->getEntityManager();
// ... do something with the Product
}
}In each event, you have access to a LifecycleEventArgs object, which
gives you access to both the entity object of the event and the entity manager
itself.
One important thing to notice is that a listener will be listening for all
entities in your application. So, if you're interested in only handling a
specific type of entity (e.g. a Product entity but not a BlogPost
entity), you should check for the entity's class type in your method
(as shown above).
Creating the Subscriber Class
A Doctrine event subscriber must implement the Doctrine\Common\EventSubscriber
interface and have an event method for each event it subscribes to:
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// src/AppBundle/EventListener/SearchIndexerSubscriber.php
namespace AppBundle\EventListener;
use Doctrine\Common\EventSubscriber;
use Doctrine\ORM\Event\LifecycleEventArgs;
// for Doctrine 2.4: Doctrine\Common\Persistence\Event\LifecycleEventArgs;
use AppBundle\Entity\Product;
class SearchIndexerSubscriber implements EventSubscriber
{
public function getSubscribedEvents()
{
return array(
'postPersist',
'postUpdate',
);
}
public function postUpdate(LifecycleEventArgs $args)
{
$this->index($args);
}
public function postPersist(LifecycleEventArgs $args)
{
$this->index($args);
}
public function index(LifecycleEventArgs $args)
{
$entity = $args->getEntity();
// perhaps you only want to act on some "Product" entity
if ($entity instanceof Product) {
$entityManager = $args->getEntityManager();
// ... do something with the Product
}
}
}Tip
Doctrine event subscribers can not return a flexible array of methods to call for the events like the Symfony event subscriber can. Doctrine event subscribers must return a simple array of the event names they subscribe to. Doctrine will then expect methods on the subscriber with the same name as each subscribed event, just as when using an event listener.
For a full reference, see chapter The Event System in the Doctrine documentation.
